Late Quaternary vertical slip rates along the Southern Yadong–Gulu Rift, Southern Tibetan Plateau

Abstract

Determination of vertical slip rate on different timescales is one of the critical issues along north-trending rifts in Southern Tibet. The Yadong–Gulu rift, a typical example of these north-trending rifts, lacked sufficient quantitative data about the vertical slip rate along its southern portion. The southern Yadong–Gulu rift is comprised of the Relong, Nieru and the Pagri–Duoqing Co grabens, which are controlled by a normal fault along its eastern boundary. To determine the vertical slip rate, we measured the average height of fault scarps along the main fault trace and dated sediments displaced by the scarps by Optically Stimulated Luminescence (OSL) dating. The results indicated that the ages of these fault scarps clustered at late Pleistocene, and the vertical separation of scarps ranged from about 5.5 m to 22 m. After abandoning distinctly inaccurate displacements, we estimate that the average vertical slip rate of Relong graben is 0.7 ± 0.1 mm/yr and Nieru graben is 0.8 ± 0.1 mm/yr, while that of Pagri–Duoqing Co graben is 2.0 ± 0.5 mm/yr since the latest Quaternary (ca. 15 ka) by weighting mean slip rate with error. It is considered that the different slip rates derive from the dispersed deformation of other faults around the Nieru and Relong graben and ductile deformation within the lower crust and northern Himalaya gneiss dome. Besides, the lack of large earthquakes in historical documents compared with the northern part of Yadong-Gulu rift, the inferred pattern of seismic migration and triggering of MHT to north-trending rifts, together indicate that the southern Yadong–Gulu rift is at high risks for middle to large earthquakes (M ≥ 6) possibly.